Since 1885, generally heralded as its date of birth, the internal combustion engine (“ICE”), the brainchild of Gottlieb Daimler, has become one of the most predominate means for propulsion and power generation through the world. Both in the sparked based combustion (e.g., gasoline powered) and compression based combustion (e.g., diesel powered) formats, the ICE has been used for propulsion and power for a variety of devices, including, but not limited to automobiles, planes, trains, submersibles, power generators, pumps and the like.
Since that inception, there has been a drive by designers of various embodiments of the ICE to generally increase its output and performance without necessarily making the engine larger. Indeed, these attempts to accomplish this objective many times generally coincides with attempts make the ICE smaller and lighter. The attempts generally include redesigning the engine components out of stronger and lighter materials or to generally adopt methods and apparatuses that push the various engines components to high performance/stress levels which may sometimes lead to breakage of those components. Various examples of these attempts may be highlighted in the field of automotive high performance/racing engines.
These developments are linked to the operation mechanicals of the various ICEs that are being sought to be improved. One area of ICE development could be the valve portion of the ICE and to the various mechanisms of the ICE which are used to control and operate those valves. Most ICEs have valves, with some exceptions being the small two-stroke ICEs used in toys and models and the Wankle rotary ICE. The ICE uses valves to regulate and otherwise control the intake of air fuel mixture into and the venting of exhaust from the inside of the combustion chamber(s) of the engine where the burning of the fuel/air mixture provides the power that operates the ICE. Generally, the combustion chamber describes that space where a piston moves within a generally enclosed portion of a cylinder.
Typically, in a valve-operated ICE, an atomized mixture of gasoline and air is generally introduced via the valves into a cylinder movably containing a piston. The piston inside this cylinder moves up and down (reciprocates) inside the bore of the cylinder and in conjunction with the timed opening and closing of the valves, draws the fuel/air mixture into the combustion chamber; compresses the air/fuel mix into the combustion chamber (for greater burning efficiency and resulting power); combusts (burns) the compressed air/fuel mixture into the combustion chamber; vents from the combustion chamber, the exhaust formed from the combusted air/fuel mixture.
A crankshaft movably connected to the pistons (rotors), converts the reciprocal movement of the pistons into the rotation power that is generally the power output provided by the ICE. The crankshaft also moveably connected (e.g., by gears, chains, and the like) to and synchronizes the rotation of a camshaft which is generally used to synchronize the opening and closing of valves relative to the position of a piston within a bore of a cylinder. The cam shaft has a plurality of cam lobes this action exposes a greater and lesser portion of the lobe to directly or indirectly open a valve. Generally, each cam lobe provides the movement for a respective valve. The shape or contour of the cam lobe and the rotational position of the lobe on camshaft generally determines the valve's operational characteristics (e.g., timing of valve operation: when the respective valve will open and closed, for how long will respective valve remain open/closed; operation characteristics of respective valve: how wide will the respective valve open). The design of the camshaft is generally very carefully engineered to ensure proper operation of the engine and has direct effect on engine performance.
Generally, there are a two basic means for connecting the camshaft(s) to the valves of an ICE, a direct connection and an indirect connection using a rocker arm assembly, which is also generally known as a valve train assembly. One type of direct connection is generally known as the flathead ICE where the valves are generally mounted in the engine block along the camshaft(s) to allow the camshaft(s) to generally directly operate the valves. Another type of direct connection is generally found in a multiple overhead cam ICE, where multiple camshafts and their corresponding sets of valves are mounted in the cylinder head, allowing the camshafts to generally directly operate their corresponding sets of the valves.
In some other types of ICE, a rocker arm assembly, or valve train assembly, acts as an intermediary between the camshaft(s) and their respective valves to allow the cam lobe movement of the camshaft to be transmitted to the respective valves thus orchestrating the movements of the respective valves. The rocker arm assembly is generally comprised in at least one embodiment of a rocker arm assembly, which is generally in movable contact with the valves, and can be in some embodiments a generally direct contact with cam lobes of a camshaft and in other embodiment is a generally indirect contact with the cam lobes of a camshaft.
The rocker arm assembly, or valve train assembly, which is generally seen as plurality of rocker arms movably connected in seesaw fashion to rocker arm holders (e.g., pedestals) generally affixed to the top of the ICE (e.g., at the top of a cylinder head).
In one type of rocker arm assembly-based ICE, a single overhead cam ICE, a single camshaft and corresponding valves are mounted on the top of a cylinder head along with a rocker arm assembly(s). As the camshaft generally indirectly turned by the crankshaft, the camshaft rotates at least one camshaft lob, which generally directly operates one end of a rocker arm to activate in see-saw fashion the other end of the rocker arm, which is generally moveably connected to a valve. In this manner, the camshaft can control the operation of its respective valves.
Another type a rocker arm assembly based ICE has the rocker arm assembly in generally in direct contact with a camshaft(s). In this type of ICE, also know as a pushrod ICE, a plurality of pushrods are used to movably connect a camshaft(s) to a rocker arm assembly. Here, generally, a camshaft(s) is located in the engine block with the corresponding valves being located in the cylinder head. A set of rods called pushrods, which are generally moveably located by a side of the ICE, moveably connects the cam lobes of a camshaft(s) to a rocker arm assembly(s) which is located on the top of the cylinder head(s).
In operation of a pushrod ICE, lifters (mechanical, hydraulic or otherwise), also known as tappets in certain applications, have a cylindrical or bucket shape with a top and bottom portions. The bottom portion rides on the top portion of the cam lobe. The bottom of the pushrod sits on or in the top portion of the lifter. As the cam lobe is generally rotated, it imparts an undulating motion to the lifter and hence to the push rod connected to the lifter.
The pushrod transmits this undulating motion to first end of a rocker arm, which is essentially in movable contact with the top of the push rod. As the first end of the rocker arm is generally pushed away by the pushrod, the second end of the rocker arm, which is generally in movable contact with one end of a valve, pushes onto the valve. This pushing action causes the head of the valve to project into the combustion chamber unsealing the valve opening for introduction of the air-fuel mixture into/venting of exhaust from the combustion chamber. (Generally speaking, a valve is designated to be either an exhaust or an air-fuel mixture valve).
As the camshaft lobe rotates away from the lifter/pushrod, this action releases pressure on first end of the rocker which lifts the second end of the rocker arm. This relieves the rocker arm's opening pressure on the valve. A spring(s) movable connected to the valve, then seats the valve back into the valve opening, reversibly sealing the valve opening shut. The spring, through the valve, also pushes up on the second end of the rocker arm.
Another area of development that can be seen generally as being related to the rocker arm assembly devolvement is the various type of shapes used for the combustion chamber. By altering the top of the combustion chamber, where generally the air-fuel mixture is compressed and combined with a spark source for the combustion, the combustion or burning of the air-fuel mixture may be improved releasing greater power and possibly reducing resulting pollutants. This alteration may be generally accomplishing by changing the size, shape of that portion of the cylinder head which forms the top of the combustion chamber.
One well-established combustion chamber shape is generally that of the essentially flat or wedged shaped topped combustion chamber. Here, the top is generally perpendicular to the sides of the combustion chamber. The bodies of the valves are generally located to be parallel to the orientation of the cylinder and piston.
A newer combustion chamber shape is generally one where the top of the combustion chamber has a half-dome or hemispherical shape. This hemispherical designation lends its name to those ICE using such as shaped-combustion chamber, HEMI-ICE. The hemispherical topped combustion chamber generally locates its valves at 45 degree angles to the cylinder/piston.
This design is generally favorable with the high performance ICE and their applications for several reasons; perceived increased burning efficiency in combustion (e.g., how well/quickly the spark(s)/resulting flame moves through the air-fuel mixture; perceived increased efficiency in moving in air-fuel mixture/venting exhaust (through the use of larger valves); perceived retention of heat for greater combustion; perceived greater pressures for improved combustion; and the like.
One of the limitations imposed by the HEMI design is that generally due to the half-dome shape, the valves are placed on angles. This means the mechanism(s) which operates the valves must essentially take into account and be able to mechanically work with these different angles. On a practical aspect, this limitation could hold down the number of valves to two valves per cylinder (whereas an ICE with a flat top combustion chamber and all its valves in the parallel orientation piston/cylinder could possibly have up to at least four valves).
A potential significant limitation in the HEMI-ICE operation is generally that the different valve angles may impose a complicated geometric application of a pushrod based gavel train assembly (which most HEMI-ICE's seem to use). For instance, as generally shown in FIG. 4, due to different valve location and angles at least one set of valves 16 (air-fuel mixture) may be located at ninety-degree angle compared the placement of their respective push rods 20a. This could lead to an inefficient or impaired movement of a pushrod 20a and a corresponding rocker arm 22a to operate the valve 16 at high speed/high performance. Such deficient valve train geometry could also impose serious limitations (via the maximum lifting that a cam shaft could provide) as to the duration of valve opening and to how open the valve could be during operation.
Some attempts to rectify this limitation have included using camshafts that have aggressive profiles (shapes) to provide cam lobes with higher and longer lifting surfaces/profiles to cause the corresponding valves to open wider for longer periods of time. When such aggressive camshafts are combined with the operational limitations imposed by the 45 degree angle placement of the valves, tremendous stress and strain on the at high speed operation result potentially leading to warping or breaking of the pushrods, rocker arms, pedestals holding the rocker arms. This warping/breakage could potentially lead to the corresponding rocker arm leading to potentially structural failure of the HEMI-ICE (e.g., the warping/breaking could cause a valve to open at the wrong time and be hit by the top of the piston with great force-resulting in possible chain reaction destruction to the piston, valve, pushrod rocker arm rocker arm pedestal, cylinder head and the like).
The cross orientation of valve and pushrod also effects the contact points between the original rocker arms and the pushrods. Both ends of the original rocker arm are in constant interference and experience exceptional frictional losses and wear.
Lack of adjustment in the original rocker arm configuration for HEMI-ICEs may also cause a great deal of problems when design changes are made to increase the valve lift and duration. When a such a compromise is instituted in the prior art for the adjusting the relationship between the “nose” of the rocker arm and the stem valve “tip,” the pushrod angle relative to the rocker arm tip may become so acute that the pushrod may come in contact with the cylinder block or may attempt to climb out of its drive “seat” in the rocker arm. The opposite action may also be true. If the pushrod angle is less severe, the rocker arm-to-valve relationship may become far from usable. This conundrum has forced racers and manufacturers to make concessions in camshaft timing, valve lift and duration, and other factors thus limiting potential of obtaining greater performance from the HEMI-ICE.
Another potential limitation is the design of a push rod-operated opposing-valve ICE where the rocker arms are placed into two groups (one group controlling the exhaust valves, another group controlling the air/fuel intake valves) with each group being movable mounted on a common shaft, both shafts mounted onto individual common pedestals that are bolted onto the top of the cylinder head. Originally, this was generally a cost-saving manufacturing measure which has turned into performance limitation issue.
As shown essentially in FIGS. 2, 4, several of these original pedestals 26 may be bolted to the top of a cylinder head 11. The original series of pedestals 26 may hold the two shafts 24 in parallel spacing, but the exhaust rocker arm shaft is held above the air/fuel mixture rocker arm shaft. The rocker arms 22a, 23a are generally gang mounted on the shafts between the pedestal mounts. Spacing springs 38 may be used to hold the rocker arms 22a, 23a in the correct spacing on the shafts 24. This prior art configuration may allow for some play for the rockers arms 22a, 23a on the shafts 24 resulting in operational irregularities. This configuration can lead to flexing and subsequent damaging of the shafts 24 and pedestals 26 as the rocker arms 22a, 23a, during high performance operation, may bend and twist under severe loading and pressure.
Another potential negative factor of this type of grouped rocker arm 22a, 23a, shaft 24 and pedestal 26 design is that to replace a single valve spring 18, common equipment in racing engines, the entire prior art rocker arm, shaft and pedestals assembly generally must be removed. The same is essentially true in the case of a damaged rocker arm 22a, 23a. Removing this entire rocker arm assembly constantly is not only monotonous but time consuming, and time is often a precious commodity in racing where runs are spaced very close together. If there is not enough time to replace damaged rocker arms or springs between runs or rounds, a race may be forfeited. If the damaged pieces are not replaced or fixed, the next run or round may be lost due to less than optimum power or worse, lead to catastrophic engine failure.
The HEMI ICE's awkward arrangement of valves and a pushrod-based rocker arm assembly could be changed through re-engineering the entire ICE, or by driving the valves via overhead camshafts. However, some applications of the high performance HEMI-ICE, such as stock car racing, must operate under rules that may dictate that the racing camshaft, valve location, valve angles must adhere to the original specifications of the car as when sold to an ordinary consumer. So any improvement thereof must only be done without changing regulated components such as the rocker arm assembly.
Other limitations of high performance ICE, including but not limited to HEMI-ICE, is that generally compressed between the bottom of the head cylinder 11 and the top of the engine block 12 is a head gasket (not shown). This head gasket generally prevents the high pressure combustion/compressed fuel air mixture of the combustion chamber from escaping and seeping into depressurized cylinders or the outside atmosphere leading to the degradation of engine performance. The head gaskets also prevent oil and coolant from passing from the head cylinder 11 and engine block 10 from leaking into cylinders and/or the outside atmosphere also leading to impaired ICE performance.
A set of studs, specially constructed and hardened metal rods with two ends that are essentially threaded to reversibly secure the rocker arm pedestals, cylinder head, head gasket and engine/cylinder block together. One end of the stud is generally threaded into a threaded aperture in the top of the engine block. The exposed threaded end of the stud generally passes through hole in the head gasket, a shaft cut into the cylinder head, to essentially pass out through the top of the cylinder head. At this point, the exposed threaded end could pass through a shaft cut through the rocker arm pedestal to come out at the top of the pedestal. A nut is threaded onto the exposed threaded end of the stud. In this manner, studs or other types of fasteners are used to tighten down and hold together the rocker arm pedestals, cylinder head, head gasket and engine block together. When due to such factors, such as very high compression pressure in a combustion chamber(s), the head gasket can rupture leading to the above described maladies.
Additionally, it is possible (due to the fact that the nut of the stud generally can only execute a pressure in a limited area on the cylinder head) that increasing size of the pressure area could help prevent the rupture of the head gasket rupture as well as prevent the possible warping of the cylinder head due to high pressure operating conditions of a particular ICE.
What is needed therefore is a rocker arm assembly for pushrod-based ICEs, including HEMI-type ICEs, that could be stronger, lighter than the present art; essentially handle the simple as well as complex valve angle geometry; generally help ameliorate the operation limitations imposed by high performance operations; and essentially increase the retaining pressure of the studs over greater portion of the cylinder head.